In conjunction with the connection of a light source such is a light emitting element exemplified by a light emitting diode with a light conductor typified by an optical fiber, there are known a connection realized by making use of an interposed lens system and a connection realized with the aid of a connector as disclosed in "OPTRONICS", No. 4, pp. 50-57 (1984), Japanese Laid-Open Patent Application No. 132110/1982 (JP-A-57-132110) and others. These known connections between the light source element and the optical fiber however require engineering skill of a high order, involving intolerably high expenditure, although loss due to the connection can be suppressed low. Further, the prior art interconnecting techniques are much limited in respect to the applicable field. As simple connecting methods, those illustrated in FIGS. 1A to 1C of the accompanying drawings are known. More specifically, according to the method shown in FIG. 1A, an light emitting diode or LED 2 constituted by a semi-conductor chip connected to lead-out wires 1 and encapsulated in a molded body of resin is directly bonded at a tip end thereof to an optical fiber by means of a bonding agent 5, the optical fiber being composed of a glass core 3 and a glass clad 4. The connection shown in FIG. 1C is similar to the one illustrated in FIG. 1A except that the tip end portion of the LED is formed flat or planar. On the other hand, the connecting structure shown in FIG. 1B is realized in such a manner in which light emitted from the LED 2 is collected by an optical lens 6 to be then directed to an end face of the optical fiber without bonding the latter to the LED.
Although the methods mentioned above rely on the simple connecting techniques, they suffer from significant transmission loss ascribable to the connection and are restricted only to specific applications. The connecting techniques in the prior art mainly concern orientation or disposition of the bonds which can ensure uniform light distribution to the individual optical fibers from the single light source (e.g. angular disposition of the optical fibers relative to the light source). By way of examples, the subject matters of the JP-A-55-7742 and JP-A-50-126438 will be considered. According to the connecting method disclosed in these publication which primarily concerns the angular disposition of the bonds for connecting the single light source to a plurality of optical fibers, there is adopted such a process as illustrated in FIGS. 2A to 2C of the accompanying drawings Referring to FIG. 2A, a plurality of optical fibers 12 have respective end faces brought into contact with the spherical surface of a spherical body 18 so that the optical axes of the optical fibers coincide with the directions normal to the spherical surfaces, respectively. After fixation by a bonding material 14, the spherical body 18 is removed, resulting in a radial array of the optical fibers, which are then connected to a light source 19 in such a manner as shown in FIG. 2B. On the other hand, in the case of the connection shown in FIG. 2C, a plurality of frustoconical members 10 each in the form of a frustrum of cylindrical cone and having a center bore formed for receiving the associated optical fiber 12. The frustoconical members 10 having the optical fibers inserted through the respective center bores are then bundled with the smaller end faces thereof being aligned with one another to thereby form a three-dimensional radial array of the optical fibers, which are then disposed in opposition to a light source 9. However, the connecting methods described above encounter difficulties in practice. In the case of the connecting method shown in FIG. 2A and 2B, for example, it is difficult to hold and maintain the individual optical fibers at respective predetermined positions with proper angles until the optical fibers are fixedly secured together by the bonding material. Besides, there arises a further problem that because the end faces of the optical fibers are likely to be contaminated by a detaching agent used for detaching the optical fiber bundle from the spherical surface of the spherical molding element 18 as well as the bonding material 14, effective utilization or transmission of light is difficult to attain. Similarly, the connecting procedure illustrated in FIG. 2C is very troublesome in practice because of necessity for preparing the frustoconical member for each of the optical fibers. Under the circumstances, the arrangement shown in FIG. 2C is not adopted in practical applications at present.
A method disclosed in JP-A-62-89914 attracts attention in that the problems pointed out above are solved to a great extent. According to this method, a light emitting or receiving element is combined with an optical fiber in an integral structure by using a same material as that of the core of the optical fiber or a material exhibiting a same refractive index as that of the core material of the optical fiber. By virtue of the integrally consolidated combination of the light emitting or receiving element with the light conductor realized according to this method, interconnection of the light emitting or receiving element and the light conductor is rendered unnecessary. Additionally, because the light emitting or receiving element is molded or encapsulated and integrally connected to the optical fiber by a silicon resin having the same refractive index as that of the core material of the light conductor, loss due to the connection can be significantly reduced. It has however been found that this method suffers shortcomings mentioned below. Certainly, this method is not accompanied with practical problems to be mentioned so long as this optical structure is used and operated at a relatively low ambient temperature in the vicinity of room temperature. However, when the optical part incorporating the light emitting or receiving element integrally combined with the light conductors in such a structure as shown in FIG. 14A is employed in the high-temperature atmosphere or environmental condition e.g. at a temperature of 130.degree. C. or higher, the core of the optical fiber protrudes from the end thereof, as is illustrated in FIG. 14B, whereby loss of light due to the leakage at the naked core portion increases significantly. Another problem is found in that delamination or cracking can take place at or in the vicinity of the interface between the light emitting or receiving element and the encapsulating resin, to incur an increase in the loss of light.